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Furnace Questions

11-06-2011, 01:29 PM

Ok, so here is my situation. I have a Lennox Pulse furnace that was installed in the mid 80's IIRC in my house. Its LP fueled and from my conversations with a HVAC guy, he said its not worth the money to convert it to NG and it would be cheaper and more cost effective to just replace it. Now, it runs fine, but I'm wondering if switching to NG is a better idea, or just to stay with LP. NG is less expensive, but once you add in the meter rental fee, hook up fee, taxes and other fees, its getting close to LP. Also, the Pulse furnaces are loud! I did some work for a customer that had a temp furnace in the forclosed half finished house he bought. I traded some tile work for it. Its a Goodman unit, looks brand new, model GMS90703BXA. Still has the warranty card registration on it. Would this be worth swapping in for the old Pulse, or just leave it alone?

The Goodman unit is a 69k BTU furnace, the Pulse is a G14Q3-80-18 (built 10/87) and is a 80k BTU unit.

Currently, I only heat ~1k sq ft of my house. The remaining ~1500 sq ft is unfinished (entire main level is gutted, very slow moving remodel project, what ever heat escapes from the basement is all that heats it) Would 69k BTU be enough for a 2500 sq ft house? If not, I have tossed around the idea to use a smaller furnace for the basement only, and when the upstairs is finished, plumb in its own unit and keep them on seperate thermostats and furnaces.

The conversion kit for the Goodman to change to LP is fairly cheap. I am past the window to have NG installed at my home before winter, but they only pay for 75' from the hook up, Im looking at 175-185' to make the hook up, so I am guessing that cost might buy a lot of LP.

My other drive for the newer unit other than its newer, and quieter, is that it has a variable speed DC Fan motor. The Pulse has a constant speed fan unit, and I leave it on 24/7. Mainly as the house tends to get stuffy in the basement without constant air flow (winters not much of a problem, mainly summer). The Goodman has a variable speed DC motor. Spins at a lower speed when either the Heat exchanger or AC pump are not in use. means quieter, and hopefully less energy use.

Some may disagree but I like Goodman's just fine. The efficiency of the 2 units are within a few points I'm sure. The Lennox was a 96% unit. The Lennox also has a factory recall for that time period on its heat exchanges. With natural gas being 1/2 that of LP around here I would swap it out in a heart beat. But 69K is a little small to attempt 2500 sq feet.

Comment

Some may disagree but I like Goodman's just fine. The efficiency of the 2 units are within a few points I'm sure. The Lennox was a 96% unit. The Lennox also has a factory recall for that time period on its heat exchanges. With natural gas being 1/2 that of LP around here I would swap it out in a heart beat. But 69K is a little small to attempt 2500 sq feet.

From what I am reading online about the model Pulse and year that I have... I probably should just replace it regardless. The 69k would be fine for just the basement as its only ~1000 sq ft, and the upstairs is no where close to being finished, probably another year or 2 so I'm not heating it. I leave one vent open to keep it around 45-50 degrees, basicly so it stays warm enough to keep pipes from feezing.

From what I am reading online about the model Pulse and year that I have... I probably should just replace it regardless. The 69k would be fine for just the basement as its only ~1000 sq ft, and the upstairs is no where close to being finished, probably another year or 2 so I'm not heating it. I leave one vent open to keep it around 45-50 degrees, basicly so it stays warm enough to keep pipes from feezing.

Then you should be good to go! I think that is the right decision for what it's worth.

Comment

Thanks JM, appreciate the response. I think I got a good deal on the Goodman furnace, basicly traded 160 bucks of material and a few hundred bucks labor for it. It honestly looks brand new, as like I said, it was only setup to keep the place from freezing.

Should I cut out the mufflers that the pulse furnace uses when swapping it? The input muffler is buried in the ceiling, so that might be impossible to remove without tearing into that, which I really don't want to do.

Thanks JM, appreciate the response. I think I got a good deal on the Goodman furnace, basicly traded 160 bucks of material and a few hundred bucks labor for it. It honestly looks brand new, as like I said, it was only setup to keep the place from freezing.

Should I cut out the mufflers that the pulse furnace uses when swapping it? The input muffler is buried in the ceiling, so that might be impossible to remove without tearing into that, which I really don't want to do.

How come I don't hear a recommendation for an energy Calc.? Isn't that step # 1 ?

What's to calculate? It's a 30year old recall Lennox vs. a Goodman variable speed 69k. The goodman will save about 50% or more on electricity with a dc motor. The change from lp to natural is another cost savings based on your area. The Goodman is also over sized for 1000 sq ft so there will be additional btus to run some upstairs.

Comment

Ok, how about this, a Goodman 115k btu, brand new furnace? Friend of mine bought it a year ago w/ a 5ton compressor unit. He traded some work for it, changed his plans on his house and just wants to sell it. Would this be a better option? My ac unit has been on the fritz for years. The 5ton is probably a little much though huh?

Comment

Now that is interesting. Depending on insulation values and a few other factors...115k would heat 2500 sq ft. You would have to make sure your duct work can handle the cfm. 5 ton of A/C is good on that footage as well, generally speaking.

Comment

Without performing a Manual J heat load calculation on your property, you are really guessing as to what size unit you need. However, when I started in the trades, approximately 36 years ago, we would always use the formula, 1 ton of a/c, or 12,000 BTU for every 600 sq. ft. of cooling space. That always worked ok on older units. In todays world of higher efficiency and the R-410a refrigerant, my son is telling me that old school method will not be accurate. I am not trying to confuse things here, just giving my experience and what worked for me.